Changes in Force and Motion
Force, Motion, and Energy
Balanced and Unbalanced Forces
A force is simply a push or a pull that can change the motion of an object. Gravity is an example of
a force that pulls objects toward each other. A box can be pushed across the floor with force, an
umbrella is pushed open with force, and wind intensity can reach such force that it can push over
trees and buildings.
Forces always come in
opposite pairs. For
example, if a force is a
push, then the opposing
force will be a pull.
If the forces on an object ARE EQUAL in size, then they are BALANCED and DO NOT cause a
change in motion.
If the forces on an object are NOT EQUAL in size, then they are UNBALANCED. Unbalanced
forces cause motion.
•  An object that is not moving starts moving when an unbalanced force is applied.
•  An object that is moving changes its speed or direction when an unbalanced force is
applied.
The size of the arrows shown on the examples below show the amount of force applied.
Notice that the forces are always shown as pairs. The direction of the arrow shows the
direction of the acting force. Remember: Balanced forces = no motion change.
Unbalanced forces = motion change.
Learn
Unbalanced - causes motion in
direction of larger force.
Balanced - no change of
motion.
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Changes in Force and Motion
Force, Motion, and Energy
Directions: Use the graphic to help you determine if the object is balanced or unbalanced.
Answer the questions for each example.
Are the forces balanced or unbalanced? ________________
Will the ball change speed or direction when acted upon by
the forces? ____________________________________
If so, draw in an arrow to show the resulting change of motion.
Are the forces balanced or unbalanced? ________________
Will the rocket change speed or direction when acted upon by
the forces? _________________________________
If so, draw in an arrow to show the resulting change of motion.
Are the forces balanced or unbalanced? ________________
Will the apple change speed or direction when acted upon by
the forces? ____________________________________
Learn
If so, draw in an arrow to show the resulting change of motion.
You draw in the force arrows. The size and direction of your
force arrows will determine if any resulting change of motion
will occur to the box. Label “no motion” or show the resulting
box motion with an arrow.
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